I have found two pages on the LHR site about the opening of T2 which will answer the inevitable questions “who and when”.
This first one indicates who and in which zone everybody will be situated(at the bottom of the page). I only question the presence of US Airways which should be passing to T3 when it becomes American Airlines.
The second page is important since it indicates the transfer date of each airline.(This shows a lot of space will be freed up at T3 so I presume all BA flights in T1 will transfer to T3 though nothing has been said so far)
And just for reference this third is the page for airlines/terminals at the moment